Sucrose, harvested primarily from sugarcane, is both a major human food as well as an important feedstock for fuel ethanol production. The commercial production of sugar may therefore benefit by either increasing the sugar content of the crop or increasing cane yield. Since increasing the sugar content of sugarcane results in increased sugar yields with a relatively small increase in associated production costs, gains in sugar content are viewed as economically more beneficial than corresponding increases in cane yield. This means that increased sugar content has become an important objective of sugarcane breeding programs and transgenic research using biotechnology-based approaches.
Many biotechnology-based approaches for increasing the reduced carbon or nitrogen content of crops are directed towards increasing the concentrations of direct precursors of the target product (Sonnewald et al., 1997; Stark et al., 1992), These approaches tend to focus on increasing the concentration of the relevant metabolites, however have never resulted in significant increases of the target metabolite in a storage organ.
A need therefore exists for an alternative method of modifying the carbohydrate content of crops such as sugar cane, and for crops such as sugar cane with a relatively higher sugar content.